1. Field of the Invention
The present invention relates to a charging and discharging control circuit and a charging type power supply device, and more particularly, to a technique for reducing the amount of time required to perform a test on the charging and discharging control circuit and the charging-type power supply device.
2. Description of the Related Art
As a conventional charging type power supply device that is formed of a secondary battery, there has been known a power supply device as shown in a circuit block diagram of FIG. 2 (for example, refer to JP 04-75430 A). That is, a secondary battery 101 is connected to external terminals −V0 and +V0 through a switch circuit 102. Further, a charging and discharging control circuit 110 is connected in parallel to the secondary battery 101. The function of the charging and discharging control circuit 110 is to detect a voltage across the secondary battery 101. In a case where the secondary battery 101 is in an over-charging state (a state in which the battery is higher than a given voltage value, hereinafter, called “over-charging protection state”) or in an over-discharging state (a state in which the battery is lower than a given voltage value, hereinafter, called “over-discharging protection state”), a signal is outputted from the charging and discharging control circuit 110 so that the switch circuit 102 turns off. Also, it is possible to stop the discharge (over-current control) when an excessive current is caused to flow in a load in such a manner that the switch circuit 102 turns off when the external terminal +V0 reaches a given voltage. Hereinafter, this state is called “over-current protection state.” The function of the charging and discharging control circuit is to protect the battery from those states.
The switch circuit 102 can be configured by an element capable of stopping the current in response to an input signal from an FET or the like. Also, there is a case in which, as shown in FIG. 3, a power supply terminal 10 for supplying a voltage to the charging and discharging control circuit 110, and a voltage detection terminal 20 for detecting the voltage across the secondary battery 101 are disposed separately. There is also a case in which the power supply terminal of the charging and discharging control circuit 110 is generally connected with a resistor 200 and a capacitor 210 as a filter so that the power supply variation attributable to the charge and discharge of the secondary battery does not induce a malfunction of the charging and discharging control circuit 110. Even in this case, a power supply terminal 10 is additionally disposed to prevent the current consumption of the charging and discharging control circuit 110 from flowing through the voltage detection terminal 20. As a result, it is possible to prevent an error from occurring in the detection voltage of the charging and discharging control circuit 110 due to the current consumption and the voltage drop that is caused by the resistor 200. The above-mentioned configuration makes it possible to enhance a detection precision for detecting a state of the secondary battery 101.
Also, in the case of controlling the charge and discharge of a lithium ion battery, there is generally employed a structure in which, in order to protect the lithium ion battery from being over-charged, a switch element of the switch circuit is turned off after a given delay time that is given by a delay circuit in a case where it is detected that a terminal voltage is equal to or higher than a given level, thereby prohibiting the charge. As a result, the charge into the secondary battery is controlled so that the over-charging state is surely detected and the secondary battery is prevented from being in the over-charging state, without corresponding to a transitional change in the battery voltage. In the charging and discharging control circuit, a control for detecting the over-discharge and stopping the current supply to a load from the secondary battery, and a control for detecting the over-current from the secondary battery to the load and stopping the current supply to the load from the secondary battery are also conducted in the same manner. The delay circuit is used even in the respective controls for the same reason. For example, in order to control the charge and discharge of the lithium ion battery, a delay time of several milliseconds to several seconds is required.
However, in a case of a charging and discharging control circuit including a delay circuit therein, a terminal that allows a delay time to be changed from an external may not be prepared due to the limit of the number of terminals provided in the circuit. In this case, when the over-charge detection voltage or the over-discharge detection voltage is tested, it takes a time equal to or longer than the delay time in the respective tests to output an output signal. A time equal to or longer than the respective delay times is required to confirm the output signal, to thereby extend the test time of the charging and discharging control circuit, resulting in an increase in the circuit manufacture costs as well as the manufacturing costs of the charging type power supply device using the charging and discharging control circuit.